In today's challenge we've got two development-stage drugmakers expecting clinical trial data before year's end: Ariad Pharmaceuticals (Nasdaq: ARIA) and Corcept Therapeutics (Nasdaq: CORT).

Which one will end up the better buy obviously depends on whether they pass their clinical trials. Let's take a look at their chances.

20 years in the making
Investors are waiting for Ariad's partner Merck (NYSE: MRK) to report phase 3 data for Ariad's cancer drug ridaforolimus later this year. The SUCCEED trial is testing ridaforolimus in patients with metastatic soft-tissue and bone sarcomas. Rather than taking the often-tried approach of going after patients that have failed other options where the bar is lower, Ariad and Merck are testing ridaforolimus as an add-on therapy in patients that did respond well to chemotherapy. As an add-on therapy, ridaforolimus would have the advantage of not having to compete with the standard treatment.

In its phase 2 trial, ridaforolimus seemed to be working against advanced sarcomas; the drug more than doubled progression-free survival -- the time it takes for the tumor to start growing again -- compared with historical averages. While that sounds good, I'd have more confidence that the phase 3 would show similar results if the drug was being compared with placebo; there's always variability between patients enrolled in a clinical trial and the historical numbers. Plus keep in mind, sarcomas aren't easily treatable; there hasn't been a drug approved in the U.S. to treat sarcoma in more than 20 years.

When all else fails, go after a rare disease
Corcept is also going after a disease that hasn't had seen a new treatment recently. In fact, there aren't any treatment options for Cushing's syndrome, a rare hormonal disorder that results in high levels of cortisol. Corcept's drug, Corlux, could have competition by the time it gets to market though; Novartis just reported positive results for its Cushing's syndrome drug, SOM230, last week.

Results from a small 50-patient trial testing Corlux in Cushing's syndrome are expected in December. The basis for testing Corlux in Cushing's syndrome is sound; Corlux blocks the GR-II receptor, which cortisol stimulates, but, as far as I can tell, this will be the first trial testing Corlux in Cushing's syndrome patients. Without any other treatment options, the bar is likely low, but whether Corcept will be able to jump over it is anyone's guess.

Beyond the lead
Ariad has the advantage when we look beyond the data for their lead drugs, although not by a whole lot.

Ariad's ridaforolimus is being tested in other tissue types. The drug targets a protein called mTOR, which is thought to be a key protein in cell survival and growth, so there's hope that it could work for cancers that are more common.

Ariad recently moved its only other clinical-stage drug, ponatinib, into a phase 2 trial. Ariad is testing the drug in two specific types of leukemia. Ariad is clearly using the trial to determine exactly which patients the drug works on; patients can have failed with Bristol-Myers Squibb's (NYSE: BMY) Sprycel or Novartis' Tasigna or have a specific mutation. But Ariad has also reached an agreement with regulatory agencies that the phase 2 trial could be enough to gain marketing approval if the data is strong enough.

Corcept has been testing Corlux in patients with psychotic depression since 2004. The drug has shown hints of working, but the trials haven't shown statistical superiority over placebo. In other words, it failed, but with just enough hope to keep Corcept going. A fourth clinical trial is ongoing, but Corcept is focusing much of its resources on the Cushing's Syndrome trial, so don't expect results this year. Even if Corlux is able to show superiority over placebo, there's so many well-established antidepressants, Eli Lilly's (NYSE: LLY) Prosac and Pfizer's (NYSE: PFE) Zoloft for instance, and antipsychotics, such as Eli Lilly's Zyprexa and Johnson & Johnson's (NYSE: JNJ) Risperdal, that one has to wonder how well it would sell.

Beyond Corlux, Corcept has one drug, CORT 108297, that the company began testing in a phase 1 trial in February. Given the marathon of drug development, CORT 108297 isn't even to its first water station yet.

With any drug developer, it comes down to risk versus reward. Both companies are fairly cheap with market caps under $400 million, so there's plenty of upside potential. Given the lack of efficacy data for Corlux in Cushing's syndrome, I'm going to have to give the advantage to Ariad in likelihood for positive clinical trial data. That isn't to say Corlux won't pass, I just think investors are going in a little blind. Ariad also has more upside potential if ridaforolimus succeeds since it might signal potential for the drug to work in other cancers.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool owns shares of Johnson & Johnson and has a disclosure policy.